Insulating (or insulated) glass (IG) units comprise two parallel sheets of glass held apart by spacer bars. The cavity formed between the sheets of glass is filled with inert gas to help reduce heat and sound transmission. Typically two different types of sealants are used to join the glass to the spacer bars. The innermost or the primary sealant joins the space bars to the glass sheets, and serves as a barrier against escape or egress of the inert gas from the cavity as well as a barrier against the entry or ingress of moisture vapor into the cavity. Thermoplastic polyisobutylene is one common primary sealant. However this material lacks mechanical strength and it exhibits comparably less adhesion than the outermost or secondary sealant. As such, one function of the secondary sealant is to provide mechanical strength to the unit and to prevent rupture of the primary sealant during the natural thermal cycles to which the unit is exposed.
Because of its good mechanical properties, polyurethane, particularly polyurethane that is based on a hydrophobic polybutadiene-based polyol, is a commonly used secondary sealant. However, such polyurethanes may not have optimal weatherability and gas retention properties. Therefore, there is a need for polyurethane based sealants that have enhanced weatherability and gas retention properties.